FIG. 1 is a cross-sectional view of a conventional bipolar transistor structure.
Referring to FIG. 1, in a conventional bipolar transistor of SBC (Standard Buried Collector) structure, an epitaxial layer (6) is formed on a p.sup.- -type semiconductor substrate (2). A n.sup.+ -type buried layer (4) is formed between the semiconductor substrate (2) and the epitaxial layer (6), and a p.sup.+ -type isolation region (8) is formed at both sides of the n.sup.+ -type buried layer (4). An n.sup.+ -type sink layer (10) is formed to be in contact with the upper part of epitaxial layer (6) and the buried layer (4). A p-type base region (12) is formed in the epitaxial layer (6) between the isolation regions (8), and an n.sup.+ -type emitter region (14) is formed in the p-type base region (12). An emitter electrode (18), a base electrode (19), and a collector electrode (20) are formed through an insulating layer (16) for respective electrical connection with the emitter (14) , the base region (12), and the sink layer (10), wherein the insulating layer (16) is formed on the epitaxial layer (6). As described above the SBC structure bipolar transistor reduces the collector resistance by forming the buried layer (4), and increases internal pressure by forming the lightly doped epitaxial layer (6) so that the bipolar transistor is a more ideal device. However, there are problems in that the production cost is increased by forming the epitaxial layer (6) and the chip size is increasing by forming the isolation region (8) separately. Also, it is difficult to reduce the chip size because of diffusion of the sink layer (10), wherein the diffusion occurs by a following annealing.
FIG. 2 is a cross-sectional view of another conventional bipolar transistor structure.
As shown in FIG. 2, in another conventional bipolar transistor of triple diffusion structure, an n-type collector region (24) is formed in a p.sup.- -type semiconductor substrate (22) and a p-type base region (26) is formed in the collector region (24). An n.sup.+ -type emitter region (28a) is formed in the base region (26), and a n.sup.+ -type collector contact region (28b) is formed in the collector region (24) of the outer portion of the extrinsic base region (26). An emitter electrode (32), a base electrode (33), and a collector electrode (34) are formed in order to respectively electrically connect with the emitter region (28a), the base region (26), and the collector contact region (28b) through the insulating layer, wherein the insulating layer is formed on the semiconductor substrate (22). As described above, there are advantages in that the production cost is relatively cheap and the chip size is relatively small because the bipolar transistor having a triple diffusion structure does not require formation of the epitaxial layer and an additional isolation region. However, the bipolar transistor has several problems, as follows. Increasing the quantity of the injecting ions, in order to reduce the collector resistance, makes the formation of the base region (26) and emitter region (28a) difficult, and the internal pressure is decreased. On the other hand, as the quantity of the injecting ions is decreased, the resistance of collector is increased.